Method of fabricating a semiconductor device

ABSTRACT

A method of fabricating a semiconductor device. A first organic layer, a sacrificial layer, and a second organic layer are sequentially formed on a substrate. Then, a photolithography process is performed for forming a predetermined pattern in the second organic layer. Thereafter, the second organic layer is utilized as an etching mask for etching the sacrificial layer till a surface of the first organic layer is exposed, thus transferring the predetermined pattern to the sacrificial layer. Subsequently, the sacrificial layer is utilized as an etching mask for etching the first organic layer till a surface of the substrate is exposed, thereby transferring the predetermined pattern to the first organic layer. Then, the sacrificial layer and the first organic layer are utilized as an etching mask for etching the substrate, thereby transferring the predetermined pattern to the substrate. Finally, the first organic layer is removed by use of plasma.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 10/063,307 filedon Apr. 10, 2002.

BACKGROUND OF INVENTION

1. Field of the Invention

The present invention relates to a method of fabricating a semiconductordevice, and more particularly, to a method of fabricating asemiconductor device through using a photoresist structure suitable forsub-micron pattern transfers in semiconductor processes.

2. Description of the Prior Art

Generally, integrated circuit production relies on the use ofphotolithographic processes and etching processes to define variouselectrical elements and interconnecting structures on microelectronicdevices. With the coming of a generation of Ultra Large Scale Integrated(ULSI) Circuits, the integration of semiconductor devices has gottenlarger and larger. G-line (436 nm) and I-line (365 nm) wave-lengths oflight have been widely used in photolithography processes. However, inorder to achieve smaller dimensions of resolution, wavelengths of lightused for photolithography processes have been reduced into deep UVregions of 248 nm and 193 nm. Nevertheless, the shorter the wavelengthsof light are, the thinner the photoresist layers are. The thinphotoresist layers might not be thick enough for blocking the etchingprocesses in the following fabrication. As a result, for aphotolithography process utilizing short wavelengths of light, it isnecessary to look for a photoresist structure suitable for lithographyprocesses and etching processes.

Please refer to FIG. 1. FIG. 1 is a schematic diagram of a prior artphotoresist structure. As shown in FIG. 1, a semi-conductor wafer 10comprises a substrate 12, an anti-reflection layer 14, and a photoresistlayer 16. Because wavelengths of light used for exposure processes arerelated to the depth of focus (DOF), a required thickness of thephotoresist layer 16 depends on the wavelengths of light. Accordingly,the thickness of the photoresist layer 16 has to be thin enough so thatthe molecules in the surface of the photoresist layer have approximatelythe same focus as the molecules in the bottom of the photoresist layer.However, the photoresist layer 16 is used to be a hard mask on thesubstrate 12 in the following etching processes. For this reason, thethin photoresist layers might not be thick enough for blocking thefollowing etching processes.

Please refer to FIG. 2. FIG. 2 is a schematic diagram of another priorart photoresist structure used to overcome the above-mentioned problem.As shown in FIG. 2, a semicon-ductor wafer 20 comprises a substrate 22,a silicon oxynitride layer 24, an anti-reflection layer 26, and aphotoresist layer 28. Therein the silicon oxynitride layer 24 serves asa hard mask so that the photoresist layer 28 together with the siliconoxynitride layer 24 can block the etching processes in the followingfabrication. After the predetermined pattern of the mask is transferredonto the substrate 22, the silicon oxynitride layer 24, theanti-reflection layer 26, and the photoresist layer 28 are removed.However, the silicon nitride layer 24 is not easy to etch away. Thus,the process of removing the silicon nitride layer 24 usually causesdamage to the surface of the substrate 22.

In addition, methods used to overcome the above-mentioned problemfurther include bilayer photoresist technology (U.S. Pat. No. 6,323,287)and top surface image (TSI) technology (U.S. Pat. No. 6,296,989).However, both of the two methods require new photoresist materials. Forexample, the photoresist layer used in the TSI technology comprisessilicon-containing materials. Providing new photoresist materials willincrease production costs and increase complexity and difficulty ofprocesses. As a result, it is necessary to look for a photoresiststructure suitable for sub-micron pattern transfers in photolithographyprocesses and etching processes.

SUMMARY OF INVENTION

It is therefore a primary objective of the claimed invention to providea method of fabricating a semiconductor device through using aphotoresist structure suitable for submicron pattern transfers insemiconductor processes so as to solve the above-mentioned problem.

According to the claimed invention, a method of fabricating asemiconductor device is provided. A first organic layer, a sacrificiallayer, and a second organic layer are sequentially formed on asubstrate. Then, a photolithography process is performed for forming apredetermined pattern in the second organic layer. Thereafter, thesecond organic layer is utilized as an etching mask for etching thesacrificial layer till a surface of the first organic layer is exposed,thus transferring the predetermined pattern to the sacrificial layer.Subsequently, the sacrificial layer is utilized as an etching mask foretching the first organic layer till a surface of the substrate isexposed, thereby transferring the predetermined pattern to the firstorganic layer. Then, the sacrificial layer and the first organic layerare utilized as an etching mask for etching the substrate, therebytransferring the predetermined pattern to the substrate. Finally, thefirst organic layer is removed by use of plasma.

It is an advantage over the prior art that the claimed inventionprovides a composite photoresist structure including a first organiclayer, an inorganic sacrificial layer, and a second organic layer. Athickness of the second organic layer can be adjusted according towavelengths of light sources used in exposure processes. Simultaneously,by adjusting thicknesses of the sacrificial layer and the first organiclayer, the composite photoresist structure is thick enough to blockfollowing etching processes. Thus, the claimed photoresist structure issuitable for sub-micron pattern transfers in semiconductor processes. Inaddition, the first organic layer is regarded as a hard mask and it iseasily removed by use of plasma. It is a further advantage that removingthe first organic layer will not damage the substrate.

These and other objectives of the claimed invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment, which isillustrated in the multiple figures and drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a prior art photoresist structure.

FIG. 2 is a schematic diagram of another prior art photoresiststructure.

FIG. 3 is a schematic diagram of a composite photoresist structureaccording to the present invention.

FIG. 4A to FIG. 4F are schematic diagrams illustrating an etchingprocess utilizing the composite photoresist structure.

FIG. 5 is a schematic diagram of a composite photoresist structureaccording to another embodiment of the present invention.

DETAILED DESCRIPTION

Please refer to FIG. 3. FIG. 3 is a schematic diagram of a compositephotoresist structure according to the preferred embodiment of thepresent invention. As shown in FIG. 3, a composite photoresist structure30 comprises a first organic layer 30 a, a sacrificial layer 30 blocated on the first organic layer 30 a, and a second organic layer 30 clocated on the sacrificial layer 30 b. The first organic layer 30 a andthe second organic layer 30 c both comprise organic materials. Thesacrificial layer 30 b comprises inorganic materials.

In particular, the first organic layer 30 a is made of low di-electricorganic materials, such as SiLK™. Additionally, the first organic layer30 a is also made of spin-on glass (SOG). Consequently, it is easy toremove the first organic layer 30 a by means of plasma, which includesoxygen (O₂), nitrogen (N₂), hydrogen (H₂), argon (Ar), C_(x)F_(y),C_(x)H_(y)F_(z), or helium (He) plasma. The sacrificial layer 30 b ismade of inorganic anti-reflection materials such as silicon oxynitride(SiON) and silicon nitride (SiN). In addition, the sacrificial layer 30b is also made of materials used for conventional hard masks, such assilicon nitride and silicon oxide. Moreover, the second organic layer 30c is made of organic photoresist materials that include positivephotoresist materials and negative photoresist materials. Furthermore,the second organic layer 30 c is made of organic materials suitable forutilizing in the e-beam lithography process. Noticeably, the compositephotoresist structure 30 is suitable for any photolithography processesin the semiconductor fabrication. It should be known by one skilled inthe art that a thickness of each of the first organic layer 30 a, thesacrificial layer 30 b, and the second organic layer 30 c could beadjusted according to requirements of processes.

Please refer to FIG. 4A to FIG. 4F. FIG. 4A to FIG. 4F are schematicdiagrams illustrating an etching process utilizing the compositephotoresist structure 30. As shown in FIG. 4A, a semiconductor wafer 40comprises a substrate 42 and the composite photoresist structure 30formed on the substrate 42. The substrate 42 is a silicon substrate, ametal substrate or a dielectric layer. Firstly, as shown in FIG. 4B andFIG. 4C, an exposure process and a development process are performed totransfer a predetermined pattern onto the second organic layer 30 c.Then, using the second organic layer 30 c as an etching mask, a dryetching process is performed on the sacrificial layer 30 b in order totransfer the predetermined pattern in the second organic layer 30 c ontothe sacrificial layer 30 b. Besides, in another embodiment of thepresent invention, the predetermined pattern can be formed in the secondorganic layer by utilizing the e-beam lithography process.

As shown in FIG. 4D to FIG. 4F, utilizing the sacrificial layer 30 b tobe an etching mask, an anisotropic etching process is performed totransfer the predetermined pattern onto the first organic layer 30 a.Then, using the sacrificial layer 30 b and the first organic layer 30 aas an etching mask, an etching process is performed to transfer thepredetermined pattern in the first organic layer 30 a onto the substrate42. While etching the substrate 42, the sacrificial layer 30 b isremoved concurrently. After transferring the predetermined pattern ontothe substrate 42, the first organic layer 30 a is subsequently removed.Up to now, the predetermined pattern on the mask is thoroughlytransferred onto the substrate 42. The first organic layer 30 a isregarded as a hard mask, and its thickness can be adjusted in order toblock subsequent etching processes. Thus, the composite photoresiststructure 30 can be used in a photolithography process utilizing lightsources with wavelengths shorter than 248 nm in deep UV regions.Furthermore, conventional hard masks are generally made out of siliconnitride or silicon oxide, which are not easy to etch away. Hence, anacidic trough is required to remove the conventional hard masks.Conversely, it is easy to remove the first organic layer 30 a throughuse of plasma. Furthermore, removing the first organic layer 30 a willnot damage the substrate 42.

Please refer to FIG. 5. FIG. 5 is a schematic diagram of a compositephotoresist structure according to another embodiment of the presentinvention. As shown in FIG. 5, a composite photoresist structure 50comprises a first organic layer 50 a, a sacrificial layer 50 b locatedon the first organic layer 50 a, an anti-reflection layer 50 c locatedon the sacrificial layer 50 b, and a second organic layer 50 d locatedon the anti-reflection layer 50 c. The first organic layer 50 a is madeof low dielectric organic materials. In addition, the first organiclayer 50 a can be made of spin-on glass (SOG). It is easy to remove thefirst organic layer 50 a by use of plasma. The sacrificial layer 50 b ismade of materials used for hard masks such as silicon nitride andsilicon oxide. The anti-reflection layer 50 c is made of organicmaterials used for organic bottom anti-reflection coating such aspolyimide and the like. Additionally, the anti-reflection layer 50 c canalso be made of inorganic materials used for inorganic bottomanti-reflection coating such as silicon oxynitride (SiON). Theanti-reflection layer 50 c can prevent incident light from reflectingfrom the substrate to the composite photoresist structure 50. Thus, dueto the anti-reflection layer 50 c, forming a standing wave in the secondorganic layer 50 d is avoided. The second organic layer 50 d is made oforganic photoresist materials that comprise positive photoresistmaterials and negative photoresist materials. As mentioned above, thecomposite photoresist structure 50 can be utilized in anyphotolithography processes. It should be known by one skilled in the artthat a thickness of each of the first organic layer 50 a, thesacrificial layer 50 b, the anti-reflection layer 50 c, and the secondorganic layer 50 d could be adjusted according to requirements ofprocesses.

In comparison with the prior art, the present invention provides acomposite photoresist structure including a first organic layer, aninorganic sacrificial layer, and a second organic layer. A thickness ofthe second organic layer could be adjusted according to wavelengths oflight sources used in exposure processes. Simultaneously, by adjustingthicknesses of the sacrificial layer and the first organic layer, thecomposite photoresist structure is thick enough to block ensuing etchingprocesses. Thus, the claimed photoresist structure is suitable forsub-micron pattern transfers in semiconductor processes. As a result,the predetermined pattern of the mask can be accurately transferred ontothe semiconductor wafer, and a critical dimension (CD) is thereforecontrolled well. In addition, the first organic layer is regarded as ahard mask and it is easily removed through use of plasma. It is also anadvantage that removing the first organic layer will not damage thesubstrate.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device may be made while retainingthe teachings of the invention. Accordingly, the above disclosure shouldbe construed as limited only by the metes and bound of the appendedclaims.

1. A method of fabricating a semiconductor device comprising: providinga substrate; sequentially forming a first organic layer, a sacrificiallayer, and a second organic layer on the substrate; performing aphotolithography process for forming a predetermined pattern in thesecond organic layer; utilizing the second organic layer as an etchingmask for etching the sacrificial layer till a surface of the firstorganic layer is exposed, thus the predetermined pattern beingtransferred to the sacrificial layer; utilizing the sacrificial layer asan etching mask for etching the first organic layer till a surface ofthe substrate is exposed, thereby the predetermined pattern beingtransferred to the first organic layer; utilizing the sacrificial layerand the first organic layer as an etching mask for etching thesubstrate, thereby transferring the predetermined pattern to thesubstrate; and removing the first organic layer by use of plasma.
 2. Themethod of claim 1 wherein the first organic layer is made of a materialselected from the group consisting of low dielectric organic materialsand spin-on glass (SOG).
 3. The method of claim 1 wherein the plasma isselected from the group consisting of oxygen (O₂), nitrogen (N₂),hydrogen (H₂), argon (Ar), C_(x)F_(y), C_(x)H_(y)F_(z,) and helium (He)plasma.
 4. The method of claim 1 wherein the sacrificial layer is madeof silicon nitride.
 5. The method of claim 1 wherein the second organiclayer is made of an organic photoresist material capable of absorbinglight sources with wavelengths shorter than 248 nm in deep UV regions.6. The method of claim 1 wherein the second organic layer is suitablefor an e-beam lithography process.
 7. The method of claim 1 wherein thesubstrate is selected from the group consisting of a silicon substrate,a metal substrate, and a dielectric layer.
 8. The method of claim 1wherein the sacrificial layer is made of silicon oxide.
 9. The method ofclaim 1 wherein the sacrificial layer is removed concurrently whileetching the substrate.
 10. The method of claim 1 wherein the methodfurther comprises forming an anti-reflection layer on the sacrificiallayer before forming the second organic layer.
 11. The method of claim10 wherein the anti-reflection layer comprises organic materials. 12.The method of claim 10 wherein the anti-reflection layer comprisesinorganic materials.